Many natural resource industry activities involve exploration for fossil fuel resources, such as oil, within a subterranean zone or formation. A pattern of impressing man-made seismic waves or "shots" is typically used to generate seismic data at different locations at different distances from the zonal interfaces. The collected data from different locations is then typically "stacked" and "migrated" to a single location to image and compare the interfaces and structures in the zone of interest in either 2 or 3 dimensions. The most promising zones of interest may then be further explored and/or natural resources recovered by methods such as drilling and mining.
Distinguishing signals is especially difficult for zones of interest near structures such as a highly fractured zone, a salt dome, or an overturned layer. An overlying salt dome can absorb reflected signals from the zone of interest.
A particularly difficult zone of interest is one containing an overturned interface underneath a salt dome. The salt dome (and the highly faulted region which typically developed on top of the salt dome) may essentially preclude conventional seismic analysis from directly above or proximate to the salt dome. As used herein, an interface capable of generating an overturned wave is typically one having a tangential angle transitioning from less than to greater than 90 degrees from the horizontal within or somewhere near the zone of interest.
It is known that laterally directed seismic reflections can turn towards the surface from the underside of an overturned interface in depth-variable velocity media, e.g., a wave initially reflected laterally downward and away by an overturned interface can be turned and detected at the surface (at some lateral distance away from the overturned interface reflection point) in a media having a seismic wave velocity gradient. In addition, methods to properly locate seismic source(s) and receiver(s) to reliably produce useful data from these overturned interfaces have not been generally available.